PROJECT SUMMARY/ABSTRACT Malaria in pregnancy remains a major challenge in Africa, where approximately 50 million women are at risk for P. falciparum infection during pregnancy each year. Among pregnant women living in malaria endemic areas symptomatic disease is uncommon, but infection with malaria parasites is associated with maternal anemia and adverse birth outcomes including abortions, stillbirth, preterm birth, low birth weight (LBW), and infant mortality. The World Health Organization (WHO) recommends the use of long-lasting insecticidal nets (LLINs) and intermittent preventive treatment with sulfadoxine-pyrimethamine (IPTp-SP) for the prevention of malaria in pregnancy in endemic areas of Africa. However, there is concern for diminishing efficacy of these interventions due to the spread of vector resistance to the pyrethroid insecticides used in LLINs and parasite resistance to SP. Thus, there is an urgent need for new strategies for the prevention of malaria in pregnancy and improving birth outcomes. Artemisinin-based combination therapies (ACTs) are now the standard treatment for malaria in Africa. Dihydroartemisin-piperaquine (DP) is a fixed-dose ACT and an attractive alternative to SP for IPTp. DP is highly efficacious, and the long half-life of piperaquine provides at least 4 weeks of post-treatment prophylaxis. Recent randomized controlled trials from our group and others showed that, compared to IPTp with SP, IPTp with DP dramatically reduced risks of malaria-specific outcomes but there were minimal differences between the SP and DP groups in risks of adverse birth outcomes. The key question motivating this proposal is why IPTp with either SP or DP is associated with similar risks of adverse birth outcomes despite the far superior antimalarial activity of DP. The likely explanation is that SP, a broad-spectrum antibiotic, protects against non-malarial causes of LBW and preterm birth. Our central hypothesis is that SP improves birth outcomes independent of its antimalarial activity and that IPTp with a combination of SP+DP will offer antimalarial and non-antimalarial benefits, thus providing superior prevention of adverse birth outcomes compared to either drug used alone. To test this hypothesis we will conduct a double-blinded randomized clinical trial in a rural area of Uganda with very high malaria transmission intensity, where our group already has an established infrastructure for clinical research. Our specific aims will be (1) to compare the risk of adverse birth outcomes among pregnant women randomized to receive monthly IPTp with SP vs. DP vs. SP+DP, (2) To compare safety and tolerability of IPTp regimens among pregnant women randomized to receive monthly IPTp with SP vs. DP vs. SP+DP, and (3) to compare risks of malaria-specific and non-malarial outcomes among pregnant women randomized to receive monthly IPTp with SP vs. DP vs. SP+DP. This study will be the first to evaluate the efficacy and safety of a novel combination of well-studied drugs for improving birth outcomes and our findings may well have important policy implications, with a change in standard practice for millions of pregnant women in Africa.